The present invention relates generally to a fishing apparatus used within a well bore to remove from the well bore broken or stuck equipment or small non-drillable materials. "Fish" is a generic name for an object to be removed and may be anything from part or all of a drill string to smaller pieces of equipment such as bit cones, pieces of tools, or any material accidentally dropped into a well bore. Even small pieces of iron pyrite, which occurs naturally in some formations, may work loose and block drilling.
In cased wells, there are various types and kinds of problems that occur which create fishing jobs, such as objects being dropped into the well, packers to be retrieved, parted tubing, collapsed casing, dropped pipe, and wirelines either parted or stuck. Some of the most common fishing problems which can occur are:
(1) Differential pressure sticking--This is a condition in which a drill stem becomes stuck against the wall of a well bore because part of the drill stem (usually a drill collar) has become embedded in filter (or wall) cake; PA1 (2) Under gauge hole--Sometimes mud filter cake builds excessively across a low pressure permeable formation. A drill string and logging tools can easily become stuck in the under gauge hole and filter cake; PA1 (3) Key seats--Key seats develop where there is a sudden change in hole deviation or above a washout in a deviated hole. Sticking usually occurs as pipe is pulled into a key seat; PA1 (4) Tapered hole--Hard abrasive formations can cause gauge wear on a drilling bit, which results in a tapered or carrot shaped hole. If a new bit is not reamed to the bottom when this situation exists, the bit will jam in the under gauge hole; PA1 (5) object alongside drill string--Occasionally, an object such as a wrench, bolt, slip or tong part, or hammer will fall into the hole alongside the drill string. Except when the drill string pulls around the object or the object can be pushed into the hole wall, serious fishing problems can develop. This is especially true if drill pipe is jammed to one side in a cased hole; PA1 (6) Inadequate hole cleaning--Inadequate hole cleaning occurs as a result of a drill string washout above the bit, low circulation rate in a large hole with an unweighted mud system, sloughing shake, a gravel bed in the shallow portion of the hole, and/or partial returns; PA1 (7) Twist off--Drill string twist-offs are a result of a faulty drill string, stress reversals in a sharply deviated hole, drilling with drill pipe in compression, and poorly stabilized drill collars; PA1 (8) Junk in the hole--Inability to make hole and/or irregular torquing after picking up a new bit indicates junk in the hole below the bit. The junk could be bit cones, float collar or wiper plug debris, rig tools, slip elements, joint (or joints) of backed off casing, or other items. In any case, the junk must be fished out of the hole.
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In clearing an object stuck downhole in a cased well, it is common practice to employ a catching or retrieving tool to obtain a hold on the stuck object, known as a fish, and a jarring tool, also called a fishing jar or simply a jar, which is capable of delivering a jarring or impact force to the fish in an effort to free it and remove it from the well bore. Designs of conventional fishing jars are of two basic types, hydraulic or mechanical, and either type is designed to deliver a single impact or jarring force to the fish during each jarring operation. A principal difference between the two types is in the method of locking and releasing a mandrel to cause the jar to impact or fire.
A fishing jar of the hydraulic type usually has a mandrel with an attached sliding valve, the mandrel fitting closely in a restricted bore in an outer housing. When a jarring force is required, tension is applied to move the mandrel relative to the housing. Fluid contained within the housing restricts movement of the mandrel relative to the housing, thereby providing a temporary delay before the mandrel is released to produce a jarring force. By increasing or decreasing initial tension applied to the jar, the resulting jarring force may be varied to some extent. When a mandrel is released, the energy stored in the stretched pipe or other operating string to which the fishing jar is connected accelerates the jar mandrel rapidly to its fully extended position against a stop. The stop converts kinetic energy of the rapidly moving mass of the pipe string into an intense jarring force which is transmitted through an overshot or spear catching tool to a stuck object or fish.
Mechanical fishing jars use a mandrel to compress a series of disk springs (instead of using trapped fluid) to restrain the movement of the mandrel relative to the housing. A latch mechanism is utilized to retain and then release the mandrel when the disk springs have been compressed to a predetermined point. As in a hydraulic fishing jar, when a mandrel is released, energy stored in the stretched fishing string accelerates the jar mandrel rapidly to its fully extended position against a stop. This sudden stop converts kinetic energy of the rapidly moving mass of the fishing string into an intense jarring force, which is transmitted to the fish.
In several of the most common fishing problems that occur, it would be a decided advantage if a fishing jar could deliver a series of rapid impact forces or blows upward against a stuck fish in order to initiate upward movement of the fish in the well bore. In a number of these fishing problems, it would be a decided advantage if a fishing jar could also deliver a series of rapid impact forces downward against a stuck fish, and then deliver a series of rapid impact forces upward against a stuck fish in order to initiate or increase upward movement of the fish in the well bore.
Accordingly, it is an object of the invention to provide an apparatus for retrieving an object stuck within a well bore, the apparatus delivering a series of rapid upward impact forces against a stuck object.
It is a further object of the invention to provide an apparatus for retrieving an object stuck within a well bore, the apparatus delivering a series of rapid downward impact forces against a stuck object or, alternately, delivering a series of rapid upward and downward impact forces against a stuck object.
It is a further object of the invention to provide an apparatus for a fishing jar operation to selectively control the number and frequency of impact forces delivered in a series of rapid downward and upward impact forces.
Accordingly, it is an object of the invention to provide method for retrieving an object stuck within a well bore by delivering a series of rapid upward impact forces against a stuck object.
It is a further object of the invention to provide method for retrieving an object stuck within a well bore by delivering a series of rapid downward impact forces against a stuck object or, alternatively, by delivering a series of rapid upward and downward impact forces against a stuck object.
It is a further object of the invention to provide a method for a fishing jar operation to selectively control the number and frequency of impact forces delivered in a series of rapid downward and upward impact forces.
It is a further object of the invention to provide a variation of intensity for each impact force delivered in series of downward and upward impact forces.
If a drill string becomes stuck in a well bore, it must be jarred loose and removed, or else the drill string must be parted and the lower segment must be fished out, ground through, or drilled around. A jar that is connected in a drill string is called a drilling jar. Accordingly, it is a further object of the invention to provide a jarring apparatus capable of being used in a drill string to deliver a series of upward jarring forces or, alternatively, to deliver a series of downward and upward jarring forces.
Yet another object of the invention is to provide a method for delivering a series of rapid impact forces to free a stuck drill string.